Magnetic powder is chiefly applied to a permanent magnet designed to provide a flux of magnetic force, a variety of magnetic sensors for detecting changed properties of a magnetic substance caused by changes of an external magnetic field to estimate changes of external physical quantities, and a storage device for storing information, such as a hard disk drive, and also used in an anti-forgery industry to generally detect changed properties of a magnetic substance and be included in a product. However, general magnetic powder is limitedly used in industries requiring light colors because the powder is dark gray or brown in color, and has a disadvantage that only the magnetic property thereof is insufficient to achieve an anti-forgery effect. Accordingly, to solve the disadvantage, a light-colored magnetic substance has been developed using a core-shell technology. This allows a magnetic particle to have characteristics of light colors such as vividness and high brightness, and thus the magnetic particle is used for a variety of products such as different colored inks, general paint, particulate pigments for vehicles, pigments for cosmetics, catalyst paint, anti-forgery inks, etc.
Accordingly, a market has required a magnetic substance that has different colors and is used for various products, and a variety of researches on technologies concealing dark colors of the magnetic substance have been conducted.
A prior art relating to concealing dark colors of the magnetic material is known in patent document 1 “WHITE POWDER AND METHOD FOR PRODUCTION THEREOF”, where in a titanium oxide membrane and a silver membrane are used to produce a light-colored magnetic substance.
However, in case of the method according to the prior art, scratches are caused on a silver membrane during an ink-making process, and thus lightness of the magnetic substance is significantly weakened. Such scratches are caused by the unique property of the silver membrane, that is, ductility. A light-colored magnetic substance is required to pass through a dispersion process in order to be used for different colored inks, general paint, particulate pigments for vehicles, pigments for cosmetics, catalyst paint, and anti-forgery inks. Accordingly, lightness of the magnetic substance is necessarily weakened when the conventional method is used, and thus the light-colored magnetic substance with such a disadvantage fails to be applied to a product. FIG. 1 shows photographs of a silver membrane that is damaged when the conventional light-colored magnetic substance is used for an ink-making process, wherein FIG. 1(a) shows a photograph of a light-colored magnetic substance before an ink-making process, while FIG. 1(b) shows a photograph of a silver membrane damaged by friction with a filler and pressure between rollers during a dispersion step of an ink-making process. When the silver membrane of the magnetic substance is damaged, reflectance drops, and thus lightness is weakened. To solve this, there is provided a solution in which a protective membrane is formed on the farthest outer surface of the light-colored magnetic substance.
In addition, in a case in which a protective membrane is generated to prevent scratches from being caused on the silver membrane, the number of the scratches is significantly decreased, while another disadvantage is caused that lightness of the magnetic substance is remarkably weakened according to refractive indexes and thickness of the protective membrane.